The invention relates to a method for automatic operation of an inflation device for motor vehicle tires.
A brief view of the world of private motor vehicles just a few ears ago would have revealed that all-wheel drive vehicles could be divided essentially into two categories, namely, high-performance and all-terrain vehicles.
On the one hand, all-wheel drive vehicles were mostly high-performance top-of-the-range variants of midquality to luxury vehicles, in which the driving torque had been distributed over two axles to reduce the load on the powertrain and to improve safety. On the other hand they were all-terrain vehicles that had been designed in the first instance for off-road use
The constant advances in the development of these vehicles, the growing range of recreational opportunities and the rising standard of living have opened the market for sport utility vehicles. These are vehicles that follow the trend of active recreational use, and also provide economy and driving comfort as well as a limited off-road capability. Many manufacturers now offer such a compromise between an all-terrain vehicle and a comfortable limousine.
These vehicles are essentially characterized by two elements: inexpensive off-road technology, which is based principally on electronic powertrain control and is not designed for prolonged use in difficult terrain, and the very generous, spacious and comfortable interior of the limousine, thus providing for comfortable travel for longer journeys as well.
The present invention is designed primarily with this category of vehicles in mind, but can be used equally effectively for pure off-road vehicles and other luxury road cars.
Particularly in the case of military off-road vehicles, the state of the art is such that vehicles are equipped with a centralized device for inflating tires. Thus the driver can increase or reduce tire pressure while travelling, either by selecting preset pressure settings typical for the terrain in question or by making an ungraduated adjustment.
The advantage of the ungraduated option consists in the ability to make the optimum adjustment with respect to the terrain over which the vehicle is travelling and the degree of loading to which it is subjected. It is also possible to compensate for the effects of temperature.
The purpose of devices of this kind is chiefly to improve traction by reducing the pressure in the tires, and thus also the specific contact pressure.
Another field of application for a tire inflation device is its comfort and stability enhancing effects. High-performance limousines in the medium and luxury class suffer from the basic problem that for reasons of driving dynamics they require a very rigid undercarriage at high speeds, whereas at lower speeds the comfort of the occupants is more important.
The object of the present invention is, therefore, to combine the two fundamental functions, traction and comfort, so that any necessary operation can be identified and carried out by sensor technology, with no driver intervention required.
This is achieve in the following manner: When the vehicle is started, the tire pressure is measured automatically and the driving conditions, whether on-road or off-road, are determined.
for road driving conditions, the speed of all four wheels is measured and a check is performed to ensure that the difference between the speeds of the wheels is within a certain tolerance,
if the difference between the wheel speeds is within the tolerance, the tire pressure setpoint is calculated, and if actual value deviates from the setpoint, the inflation or deflation valve is activated until the setpoint is reached and established,
if the difference between the wheel speeds is not within the tolerance, the driving speed is measured as for off-road driving conditions and this is compared with a threshold value,
if this threshold value is not exceeded, the deflation valves are activated and a tire pressure that is still permissible is established.
The tire pressure is measured each time these steps are completed, and the cycle is then repeated from the beginning.
This method provides automatic monitoring of driving conditionsxe2x80x94off-road or street drivingxe2x80x94by monitoring any reduction gear switch and/or the level sensors (if the vehicle is equipped with a ride leveler) for frequent movements of the vehicle, and/or the wheel revolution differences and/or differential locks and/or a manually operated traction selection switch.
The method according to the invention provides automatic adjustment of tire pressure according to speed and load on the basis of various sensor signals, and also significant traction control in off-road use. The need for intervention to increase traction is determined on the basis of sensor signals. A logic circuit links information about differing wheel revolutions, required reduction gears and differential locks of many different types. Information from electric differential locks, limited slip differentials and positive engagement locks can be processed.
The most important feature of the present invention is that the entire system effectively operates automatically without driver intervention to calculate the correct tire pressure, based on measurements of axle load, driving speed and traction requirement/driving surface conditions, but certain settings can be made manually if the driver so wishes.